How would you determine if a project is likely to produce an AGI or if
certain builder(s) are likely to make an AGI given that there is no
successful AGI to date to use as a benchmark for comparison?

Would you decide? Simply based on your opinion of how an AGI should be? Or
are there any more objective signs to look for?

Last question, how would you prove that your AGI idea (if you have one) is
likely to produce an AGI?

Keep in mind, I'm not talking about finished superhumanly intelligent AGIs.
Those are easy to prove. (In fact, I'm suspicious of claims of having a
superintelligent AGI without a Singularity or at least some nice discoveries
to back that up.) I'm talking about pre-AGI claims of AGI potential. (They
will often ask for your money.)